Russian President Vladimir Putin has said the chemical attack in Syria was a sly provocation by the rebels.

VALDAI, Russia — Russia has strong grounds to believe that Syrian rebels were responsible for the country’s chemical attack, President Vladimir Putin said Thursday — a claim almost universally disputed by Western governments.

Speaking at a conference, Putin said “we have every reason to believe that it was a provocation, a sly and ingenious one.” He added, however, that its perpetrators have relied on “primitive” technology, using old Soviet-made ammunition no longer in the Syrian army’s inventory.

The U.S., Britain, France and others believe that a report by U.N. inspectors has proven the attack was conducted by the Syrian military. The U.N. report released Monday confirmed that chemical weapons were used in the attack, but did not ascribe blame.

Putin expressed optimism when asked whether he trusts Syrian President Bashar Assad to fulfill Russia’s plan for Syria to surrender its chemical weapons and avoid a U.S. strike. He said Damascus’ actions so far have given reason to believe the initiative will be implemented.

“I can’t be 100 percent sure that we will bring it to the end, but what we have seen in the past few days has given us confidence that it will be accomplished,” Putin said.

Responding to a question about what would happen if Assad’s government breaks its pledge, Putin said “we have no reason to believe they would fail to fulfill their obligations.” “We will look into that if they would, but it’s premature to talk about it,” he added.

Asked if Syria’s list of its chemical arsenals could be trusted, Prime Minister Dmitry Medvedev said Damascus will “have to do its best to convince the international community that the list they present is complete and that efficient verification and control can be provided.”

Speaking in Moscow, Medvedev sought to emphasize that Russia shouldn’t be held solely responsible for the plan’s success.

“The responsibility (for success of the plan) has not shifted to the Russian federation,” Medvedev said. “It’s our joint responsibility” and not “the sole responsibility of the Russian federation.”

Putin insisted that Russia strongly opposed a U.S. attack on Syria because it would violate basic principles of international law and undermine the U.N. role, not because it was trying to keep Assad in power.

“We don’t have some exclusive interests in Syria which we would seek to protect by defending the current government,” Putin said. “We are striving to preserve the principles of international law.”

He said that during his discussions with Western leaders they have failed to answer his question about what the West would do if al-Qaida-linked militants finally unseat Assad and come to power in Syria.

“What sense does it make to launch a strike if you don’t know how it will end?” Putin said.